A middle-aged woman with newly diagnosed autoimmune hepatitis on high-dose prednisolone (50 mg daily) presented acutely with 3 days of fever with headache, followed by an acute change in mental state a day before hospitalisation. Clinically, she was slightly drowsy (GCS = 12) and disoriented, with neck stiffness and photophobia. The urgent non-contrast CT head was normal, and her white blood cell count (WBC) was elevated at 21,000/ml of blood (mostly neutrophils). She was prescribed intravenous vancomycin, ceftriaxone, ampicillin and acyclovir, and lumbar puncture was performed 3 hours after arrival at the hospital (we don’t have the efficiency of many developed countries in this respect, where lumbar punctures are often performed down at the emergency department!). This showed cerebral spinal fluid (CSF) pleocytosis with 880 WBC/ml of CSF – mostly lymphocytes.

The next day, the Microbiology Laboratory reported the growth of a Gram-positiverod from the anaerobic blood culture bottle.

Question 1: What is the likely cause of her infection?

Question 2: What antimicrobial agents would you recommend for the treatment of the infection?

[Updated 28th February 2015]

In this context, given the immunosuppression, clinical presentation of meningo-encephalitis, and the presence of Gram-positive rods from the anaerobic bottle, the patient very likely (and actually did) have Listeria monocytogenes bacteraemia with meningo-encephalitis.